A conventional linear motor system includes, as a moving element, permanent magnets that serve as magnetism loading means; and as a stator, windings that serve as electricity loading means. A plurality of windings are arranged in a stroke direction, and controllers are respectively provided for supplying a current to the windings and are connected to an interval switching device (see, for example, patent document 1).
The conventional linear motor system will now be described while referring to FIG. 14.
In FIG. 14, reference numeral 900 denotes a conventional linear motor system; 901, a moving element; 902, permanent magnets; 903, stators; 904, controllers; and 905, an interval switching device. Windings that serve as electricity loading means are provided for the stators 903, which are respectively connected to the controllers 904. When the controllers 904 supply a current to the stators 903, thrust is generated between the stators 903 and the moving element 901, so that the moving element 901 is moved in the stroke direction. The interval switching device 905 is a device that employs positional information, relative to the moving element 901, obtained from specific means for measuring the position of the moving element 901, and provides a current supply instruction only for the controller 904 that is connected to the stator 903, which is located opposite the moving element 901 and contributes to the generation of a thrust.
As described above, according to the conventional linear motor system, of the controllers 904 connected to the stators 903, the internal switching device 905 issues an instruction to a controller 904 connected to a stator 903, which contributes to the generation of a thrust, so that a current is to be supplied only to a desired stator 903. Therefore, since a current does not flow to stators 903 that do not contribute to the generation of a thrust, generation loss is reduced and a longer stroke is obtained, with power saving.
However, for the above described conventional linear motor, to extend a stroke the stators 903 must be arranged across a distance equivalent to a desired stroke, and the same number of units as that of the stators 903 is also required for the controllers 904 to be connected to the stators 903. The controller 904 is generally expensive, and a problem exists with costs when the controller 904 is employed to extend a stroke.
Furthermore, the interval switch device 905, for issuing a current supply instruction to the controller 904, must obtain the exact position of the moving element 901 that moves in the stroke direction, and must provide a current supply instruction for a controller 904 that is connected to a stator 903 that faces the moving element 901 and that contributes to the generation of a thrust. Additionally, this instruction must include the magnitude, the phase and the frequency of a current. Therefore, there is a problem in that control of the interval switching device 905, relative to the controllers 904, is very complicated.
Further, for the conventional linear motor system 900, there is a difference in an induced voltage and the inductance between the state wherein the moving element 901 is positioned between the adjacent stators 903 and the state wherein the moving element 901 is positioned entirely opposite a stator 903. Therefore, as a problem, when the controller 904 supplies a current to the stator 903, the induced voltage and the inductance differ in accordance with the position of the moving element 901, relative to the stators 903, so that deterioration of the control performance and speed fluctuation occur.
Also, generally, linear motors are roughly classified into a moving armature type linear motor and a fixed armature type linear motor.
For a moving armature type linear motor, the stator side is constituted by permanent magnets and a secondary conductor, and the moving element side is constituted by armature windings (see, for example, patent document 2). In this case, a servo amplifier for driving a linear motor is connected to the moving element, and since, as well as for a rotary type motor, this arrangement can be handled as is a motor block, motor control of the moving armature type is easily exercised.
On the other hand, for a fixed armature type linear motor, the stator side is constituted by a linear motor stator and armature windings and the moving element side is constituted by permanent magnets and a secondary conductor (see, for example, patent document 3). In this case, a servo amplifier for driving a linear motor is connected to the stator side. As for the case involving a long stroke, a series connection of a plurality of armature windings and a parallel connection of a plurality of armature windings are proposed as arrangements for stator side armature windings. And in the case of a series connection, all the intervals, including an interval where a moving element does not overlap, are rendered conductive. While in the case of a parallel connection, switching between intervals is required for each block of armature windings, in accordance with a movement of the moving element.
As an interval switching method, there is a method whereby linear motor driving servo amplifiers, in a count equivalent to the number of stator blocks, are prepared, so that one servo amplifier controls one stator, and the servo amplifiers are switched, or a case wherein the control process is performed by one servo amplifier, or a small number of servo amplifiers, and an interval selection switch is provided separately, from the servo amplifiers, to exercise the control.
Patent Document 1: JP-A-3-45147 (fourth column, FIG. 5)
Patent Document 2: JP-A-2001-78420
Patent Document 3: JP-A-2000-224833